Transcranial magnetic stimulation (“TMS”) uses an induction coil to induce an electric field (“E-field”) within the brain. The locations of the brain exposed to a strong enough E-field will became activated, or stimulated. In navigated brain stimulation (“NBS”), the E-field induced in the brain by a TMS induction coil device is graphically represented on a display. As part of NBS, a three-dimensional (“3D”) localization system is used to locate the TMS coil device accurately with respect to a subject's head. The localization system correlates TMS coil device location information with anatomical information representative of a subject's brain, which typically is obtained from magnetic resonance imaging (“MRI”) of the brain. The E-field information is shown as an overlay on a graphical display of the subject's brain generated from the MRI images of the brain. By viewing the display, the user can interactively position the TMS coil device, in real time, in relation to the brain to stimulate a desired location of the brain.
A TMS induction coil device typically includes coils having 5 to 30 loops (windings) of capper wire located in a casing. The windings are normally circularly shaped or in the form of a figure 8. The shape, and the location of the maximum, of the E-field induced in the brain depend on the exact shape of the coil windings within the TMS coil device and their location and orientation with respect to the brain. In NBS, the strength and location of the E-field induced in the brain by the TMS coil device is determined from information representative of the location and orientation of the casing of the TMS coil device in relation to the brain and the location and orientation of the coil windings within and in relation to, respectively, the casing. The location and orientation of the casing is obtained from a navigation or tracking device, such as an infrared tracking device including an infrared transceiver and infrared reflective elements attached to the TMS coil device, that tracks the movement of the casing, as is conventional in the art. The location and orientation of the coil windings within the casing are determined by generating a model of the coil windings within the casing of the TMS coil device using information obtained from, for example, X-ray images of the casing of the TMS coil device.
It is known that, in NBS, navigation accuracy and the accuracy of the determination of the E-field induced in the brain are greatly affected by any inaccuracies associated with the tracking of the location of the coil windings within the TMS coil device with respect to the brain. Current prior art TMS coil devices, however, do not provide that a tracking device, such as, for example, a tracking device including three infrared reflective elements positioned at a predetermined orientation and spacing with respect to one another as is conventional in the art, is at a predetermined location and orientation or rotation angle on the casing of the TMS coil device each time that the tracking device is attached to the TMS coil device, such that the location and orientation of the reflective elements in relation to the casing are fixed.
For example, current TMS coil devices do not include a firm and solid coupling structure to which a tracking device can be attached conveniently and with ease, and where the coupling structure would substantially maintain its shape even after the tracking device has been repeatedly attached to and detached from the coupling structure. In the prior art, a tracking device is typically attached to a handle extending from the casing of a TMS coil device. The handle usually is a round, tubular plastic part having a relatively thin wall thickness. The rounded shape of the handle permits the tracking device to rotate easily about the handle, should a clamp securing the tracking device to the handle loosen even slightly. Further, based on the thin wall thickness of the handle, an originally round handle of a TMS coil device has been known to flatten slightly after repeated attachment and detachment of the tracking device.
Thus, the construction and configuration of handles of prior art TMS coil devices which the tracking device is attached to and detached from do not provide that the tracking device can be repeatedly attached to the TMS coil device at the same location and orientation in relation to the casing of the TMS coil device, and consequently to the coil windings in the casing. Each time that a tracking device is attached to a handle of a prior art TMS coil device, or sometimes following prolonged use of the TMS coil device with the tracking device attached thereto, a calibration must be performed to determine the location and orientation of the reflective elements of the tracking device in relation to the casing, and thus to the coil windings contained in the casing. The need for repeated calibration of the tracking device is undesirable. Furthermore, the possibility that the tracking device does not remain calibrated with respect to the casing, following an initial calibration when the tracking device is attached, can cause inaccuracies in the representation of the position and orientation of the casing in relation to the brain, and thus inaccuracies in the position of the E-field induced on the brain represented on a display as part of NBS performed with the TMS coil device, which are not known to the user during use of the TMS coil device.
Further, prior art TMS coil devices are ordinarily sold without any accompanying information that identifies locations on the casing of the TMS coil device which constitute fixed points of reference that can be used in connection with information obtained from a tracking device attached to the TMS coil device to accurately track movement of the TMS7 device in relation to the subject's head.
Therefore, there exists a need for a TMS coil device having an attachment portion which a tracking device can be repeatedly attached to and detached from with relative ease, and where, when the tracking device is attached to the attachment portion of the TMS coil device, the tracking device is at substantially the same, predetermined location and orientation in relation to the casing, and consequently the coil windings in the casing.